Hemodialysis treatment is a blood treatment purifying extracorporeally circulating blood of a patient. In hemodialysis treatment, a dialyzer is used as a blood purification instrument for flowing therethrough a dialysate, and a blood circuit for extracorporeally circulating blood of a patient is connected to the dialyzer through which the blood and the dialysate contact each other via dialysis membranes within the dialyzer so as to remove waste materials and excess water in blood (the removal of excess water is usually called as “ultrafiltration”). The blood purified by the dialyzer is returned into a body of a patient and, on the other hand, the blood waste material and excess water are discharged outside, together with the dialysate, via a dialysate discharging line.
The waste materials removed from blood contain urea, uric acid, creatinine etc. and variations of the concentration of urea in blood is an effective indicator of dialysis efficiency. Accordingly, it has been proposed to monitor the variation in urea concentration to obtain proper dialysis efficiency. Although it is usually possible to know the variation in the urea concentration via a regularly performed blood examination, it is impossible to monitor the variation in urea concentration in real time during a dialysis treatment.
Accordingly, it has been proposed to arrange a discharged liquid concentration sensor on a dialysate discharging line so as to detect the variation in urea concentration (i.e. an indication such as “Kt/V”) in real time (see e.g. JP 2002-516722 below). Such a conventional discharged liquid concentration sensor usually comprises LED(s) (light emitting means) for irradiating light on to discharged liquid from a dialyzer, a light receiving element(s) (light receiving means) for receiving light from the LED(s) transmitted through the discharged liquid, and a detecting means for detecting a received light intensity received by the light receiving element(s) and is structured so that the concentration of discharged liquid can be detected based on the received light intensity detected by the detecting means.
However, in the blood purification apparatus of the prior art, there is concern that the discharged liquid concentration sensor is liable to be influenced by heat within a dialysis apparatus body and thus an error in the detection of concentration may be increased since the discharged liquid concentration sensor is arranged on a dialysate discharging line within the dialysis apparatus body. In particular, since liquids (dialysate and cleaning liquid) are warmed or heated (the cleaning liquid is boiled water), large temperature variation within the dialysis apparatus body is caused. Thus, values of resistors of a light emitting means e.g. of a discharged liquid concentration sensor would be varied and accordingly the emitting light intensity would be greatly varied.
It is, therefore, an object of the present invention to provide a blood purification apparatus that can minimize the detection error of liquid concentration caused by temperature variation and thus improves the accuracy of detection of liquid with a concentration detecting means.